JP4711736B2 - Electroabsorption modulator and semiconductor device - Google Patents

Description

  The present invention relates to an optical modulator in an optical communication system, and in particular, an electroabsorption modulator (EAM: Electro-Absorption Modulator) that can arbitrarily modulate laser light according to the intensity of an applied voltage, and The present invention relates to a semiconductor device in which an electroabsorption modulator is formed.

  The following Patent Documents 1 to 3 are all related to a semiconductor device in which a laser part and an electroabsorption modulator part are integrated on a semiconductor substrate. As described in these documents, the electroabsorption modulator can be manufactured by a semiconductor manufacturing technique.

Japanese Patent Laid-Open No. 10-163568 JP-A-9-139551 JP-A-10-256669

  When a voltage is applied to the light absorption layer existing between the anode and the cathode of the electroabsorption modulator, a light absorption phenomenon occurs in the electroabsorption modulator. Then, a pair of electrons and holes is generated due to the occurrence of the light absorption phenomenon. The generated electrons and holes can be taken out as a current through the anode and the cathode. This current is called photocurrent. Note that the amount of light absorption in the electroabsorption modulator varies depending on the value of the voltage applied to the light absorption layer due to the external voltage applied between the anode and the cathode.

  A resistance exists in the direction between the anode and the cathode of the electroabsorption modulator. When the generated photocurrent passes through this resistor, a voltage drop occurs. Then, when a voltage is applied between the anode and the cathode of the electroabsorption modulator, the voltage applied to the light absorption layer decreases due to the voltage drop in this resistance.

  When the laser part and the electroabsorption modulator part are formed adjacent to each other on the semiconductor substrate as in the techniques described in Patent Documents 1 to 3, the light emitted from the laser part is changed to the electric field on the side of the laser part. The light enters the absorption modulator section. For example, taking the case of Patent Document 1 as an example, light travels in the extending direction from the upper right to the lower left of the LD section ridge waveguide 111 in FIG. Is incident on.

  The incident light is absorbed by the electroabsorption modulator unit due to the light absorption phenomenon, so that the light intensity decreases with the progress in the electroabsorption modulator unit. For example, taking the case of Patent Document 1 as an example, the intensity of the light decreases as the light travels in the modulator ridge-shaped waveguide 112 in FIG.

  Therefore, per unit length of the light traveling direction (corresponding to the extending direction from the upper right to the lower left of the modulator ridge-shaped waveguide 112 in FIG. 2 of Patent Document 1) generated in the electroabsorption modulator. The intensity of the photocurrent also decreases as the light travels in the electroabsorption modulator section.

  On the other hand, in the semiconductor laminated structure constituting the electroabsorption modulator part, the thickness, composition, carrier concentration, etc. of each layer are usually produced uniformly in the light traveling direction. Therefore, the resistance value in the anode-cathode direction per unit length in the light traveling direction is constant in the light traveling direction.

  Then, the value of the voltage drop, which is the product of the photocurrent that varies depending on the position in the light traveling direction and the resistance that has a constant value in the light traveling direction, is large at the position near the laser section in the electroabsorption modulator section. Thus, the value is small at a position away from the laser portion. This means that the voltage applied to the light absorption layer (that is, the value obtained by subtracting the voltage drop due to resistance from the externally applied voltage) varies depending on the position in the light traveling direction in the electroabsorption modulator section.

  In the electroabsorption modulator, it is desirable that the voltage is uniformly applied to the light absorption layer at all positions in the light traveling direction. This is because if the voltage application to the light absorption layer is uniform, the extinction characteristic of the optical modulator (the characteristic of steep change of the light intensity with respect to the change of the external applied voltage) is improved.

  However, in the conventional electroabsorption modulator, the voltage applied to the light absorption layer differs depending on the position in the light traveling direction due to the phenomenon described above, so that the quenching operation becomes non-uniform, and the extinction characteristic is steep. Could not be obtained sufficiently.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an electroabsorption modulator with improved extinction characteristics and a semiconductor device in which the electroabsorption modulator is formed.

  The present invention provides a semiconductor substrate and light absorption formed above the surface of the semiconductor substrate that can absorb a part of incident light by applying a voltage and outputs the incident light in a predetermined direction. A layer, a semiconductor layer formed on the surface of the light absorption layer, an anode formed on the surface of the semiconductor layer, and a cathode formed on the back surface of the semiconductor substrate. A plurality of semiconductor layer regions having different resistance values in the direction between the anode and the cathode are included, and a photocurrent based on the incident light is generated in each of the plurality of semiconductor layer regions, and in each of the plurality of semiconductor layer regions In the semiconductor layer region where the intensity of the photocurrent is relatively larger than the intensity of the photocurrent in the other semiconductor layer region, the resistance value in the direction between the anode and the cathode is relatively small. Further, in each of the plurality of semiconductor layer regions, in the semiconductor layer region where the intensity of the photocurrent is relatively smaller than the intensity of the photocurrent in the other semiconductor layer region, the direction between the anode and the cathode This is an electroabsorption modulator having a relatively large resistance value.

  According to the present invention, in each of the plurality of semiconductor layer regions, the resistance in the direction between the anode and the cathode is increased in the semiconductor layer region in which the intensity of the photocurrent is relatively larger than the intensity of the photocurrent in the other semiconductor layer regions. In the semiconductor layer region, the resistance in the direction between the anode and the cathode is relatively small, and in each of the plurality of semiconductor layer regions, the photocurrent intensity is relatively small compared to the photocurrent intensity in the other semiconductor layer regions. The value of is relatively large. Therefore, it is possible to make the voltage drop calculated by the product of the photocurrent and the resistance uniform at each position in the traveling direction of the incident light, and the voltage applied to the light absorption layer is uniform in the traveling direction of the light. It is possible to approach. Thereby, an electroabsorption modulator with improved extinction characteristics as an optical modulator can be obtained.

<Embodiment 1>
The present embodiment is an electroabsorption modulator including a semiconductor layer including a plurality of semiconductor layer regions having different resistance values in the direction between the anode and the cathode, and a semiconductor device in which the electroabsorption modulator is formed. .

  FIG. 1 is a diagram showing a semiconductor device according to the present embodiment. As shown in FIG. 1, the semiconductor device includes an electroabsorption modulator MD formed on a semiconductor substrate 100, and a laser LD formed on the semiconductor substrate 100 adjacent to the electroabsorption modulator MD. It has. The semiconductor substrate 100 is an n-type InP substrate, for example.

  An n-type InP guide layer 101 is formed on the surface of the semiconductor substrate 100. In the laser LD, an InGaAsP laser active layer 102 and a p-type InP guide layer 103 are stacked on an n-type InP guide layer 101. In the electroabsorption modulator MD, an InGaAsP light absorption layer 104 is formed on the n-type InP guide layer 101.

  A p-type or i-type InP guide layer 105 and a p-type InP guide layer 110 having a lower resistance value than the p-type or i-type guide layer 105 are formed on the InGaAsP light absorption layer 104. The p-type or i-type InP guide layer 105 and the p-type InP guide layer 110 are arranged in the traveling direction D1 of incident light from the laser LD, and the impurity concentration in the p-type InP guide layer 110 is p-type. Alternatively, the impurity concentration in the i-type InP guide layer 105 is higher.

  A p-type InP cladding layer 106 is formed on the p-type InP guide layer 103, the p-type InP guide layer 110, and the p-type or i-type InP guide layer 105. In the laser LD, a p-type InGaAs contact layer 107a is formed on the p-type InP cladding layer 106, and in the electroabsorption modulator MD, a p-type InGaAs contact layer 107b is formed on the p-type InP cladding layer 106, respectively. Has been.

An SiO ₂ insulating film 108b is buried between the p-type InGaAs contact layers 107a and 107b, and the p-type InGaAs contact layers 107a and 107b are insulated from each other. In addition, SiO ₂ insulating films 108a and 108c are formed at the ends of the p-type InGaAs contact layers 107a and 107b, respectively.

  Anodes 109a and 109b are formed on the p-type InGaAs contact layers 107a and 107b, respectively. A cathode 117 is formed on the back surface of the semiconductor substrate 100.

  In the present application, the guide layers 105 and 110, the cladding layer 106, and the contact layer 107b from the top of the InGaAsP light absorption layer 104 to the anode 109b in the electroabsorption modulator MD are collectively referred to as a semiconductor layer. In this semiconductor layer, as shown in FIG. 1, there are a first semiconductor layer region having a resistance R1 between the anode and the cathode, and a second semiconductor layer region having a resistance R2 in the same direction. Exists. The resistance R1 is a resistance straddling the guide layer 110, the cladding layer 106, and the contact layer 107b, while the resistance R2 is a resistance straddling the guide layer 105, the cladding layer 106, and the contact layer 107b.

  In the present embodiment, since the impurity concentration in the p-type InP guide layer 110 is higher than the impurity concentration in the p-type or i-type InP guide layer 105, the values of the resistors R1 and R2 in the semiconductor layer are different. That is, the value of the resistance R1 at a location where the light intensity of the incident light is relatively large is small, and the value of the resistance R2 at a location where the light intensity of the incident light is relatively small.

  A case where a light absorption phenomenon occurs in the electroabsorption modulator MD will be described. First, laser light is generated in the InGaAsP laser active layer 102 of the laser LD, and the laser light travels in the traveling direction D1. Then, the laser light enters the InGaAsP light absorption layer 104 of the electroabsorption modulator MD.

  The cathode 117 is supplied with the ground potential GND, and the anode 109b of the electroabsorption modulator MD is supplied with the external voltage V1 generated by the high-frequency power source PS via the resistor Ra. A voltage is applied to the InGaAsP light absorption layer 104 in accordance with the application of the external voltage V1.

  When a voltage is applied, the InGaAsP light absorption layer 104 absorbs part of incident light, and a light absorption phenomenon occurs. Thereby, the laser beam generated by the laser LD is modulated. Incident light further traveling in the traveling direction D1 is output from the right end surface of the InGaAsP light absorption layer 104 in FIG.

  Due to the occurrence of the light absorption phenomenon, photocurrents Iph1 to Iph3 based on incident light are generated at various locations in the first and second semiconductor layer regions of the electroabsorption modulator MD. In FIG. 1, the size of the arrows indicating the photocurrents Iph <b> 1 to Iph <b> 3 decreases as the laser light enters from the incident side toward the emission side. This means that the current value of the generated photocurrent decreases as it proceeds from the incident side to the emission side. The current value of the photocurrent gradually decreases in this way because the laser light incident on the electroabsorption modulator MD is absorbed and the light intensity decreases as it progresses.

  FIG. 2 is a graph showing the relationship between the photocurrent and the distance in the electroabsorption modulator MD. In FIG. 2, the vertical axis represents the current value Iph (x) per unit length in the traveling direction D1 of the photocurrent, and the horizontal axis represents the distance from the incident end surface to the traveling direction D1 in the electroabsorption modulator MD of FIG. x is taken. As shown in FIG. 1, x = 0 at the incident end face and x = x1 at the outgoing end face in the electroabsorption modulator MD. Further, x = x2 is set at the boundary portion between the guide layers 105 and 110.

  As shown in FIG. 2, the current value Iph (x) of the photocurrent gradually decreases as it proceeds from the incident end face to the exit end face. This corresponds to a change in the size of the arrow indicating the photocurrents Iph1 to Iph3.

  3 does not have separate resistance values in the anode-cathode direction like the guide layers 105 and 110 in FIG. 1, but has a uniform resistance value in the anode-cathode direction from the incident end face to the exit end face. 6 is a graph showing a relationship between an applied voltage between an anode and a cathode and a distance in the electroabsorption modulator in a conventional electroabsorption modulator including a guide layer having λ. Here, in order to simplify the explanation, the resistance between the high-frequency power source and the modulator, such as the resistance Ra in FIG. 1, is ignored. Then, the value of the voltage applied between the anode and the cathode becomes equal to the external voltage V1 generated by the high frequency power supply. In FIG. 3, the case where the external voltage V1 is a negative value is taken as an example.

  Considering the constituent components of the anode-cathode voltage V1, it can be roughly divided into an applied voltage to the light absorption layer and an applied voltage to the semiconductor layer composed of the guide layer, the cladding layer, and the contact layer.

  Since the resistance exists in the semiconductor layer as described above, if this is R, the product Iph (x) × R of the photocurrent Iph (x) and the resistance R is the voltage drop amount in the semiconductor layer. Therefore, the remaining value VMQW obtained by subtracting the voltage drop amount Iph (x) × R in the semiconductor layer from the anode-cathode voltage V1 becomes the voltage applied to the light absorption layer.

  Since the current value Iph (x) of the photocurrent decreases as the distance x increases, the value of the voltage drop Iph (x) × R in the semiconductor layer is also conventional in the section where the resistance R is x = 0 to x1. As shown in FIG. 3, a graph similar to the current value Iph (x) in FIG. 2 is obtained.

  That is, as described in the section of the problem to be solved by the invention, if the resistance R is constant in the section of x = 0 to x1, the photocurrent Iph (x) having a different value depending on the position in the traveling direction D1. The voltage drop Iph (x) × R accumulated with the resistance R having a constant value in the traveling direction D1 is a large value near the laser LD in the electroabsorption modulator MD, and a position away from the laser LD. Then it becomes a small value. As a result, the voltage VMQW applied to the light absorption layer differs depending on the position of the light traveling direction D1 in the electroabsorption modulator MD.

  Here, in the conventional electroabsorption modulator in which the resistance R is constant in the section of x = 0 to x1, and in each position x = 0 to x2, x2 to x1 in the traveling direction D1 of the incident light, Comparison is made with the electroabsorption modulator MD of the present embodiment in which the resistance values are different from those of R1 and R2.

  FIG. 4 is a diagram comparing the conventional electroabsorption modulator shown in the graph of FIG. 3 with the electroabsorption modulator MD of the present embodiment. In the electroabsorption modulator MD of the present embodiment, the region where x = 0 to x2 is the region A, and the region where x = x2 to x1 is the region B.

  If the value of the resistor R is constant as in the conventional case in the section of x = 0 to x1, the value of the voltage drop Iph (x) × R continuously from x = 0 to x = x1 as in FIG. Gradually decreases (decreasing broken line graph in FIG. 4). On the other hand, in the electroabsorption modulator MD of the present embodiment in which the resistance value in the semiconductor layer is different from those of R1 and R2, the same voltage drop Iph (x) × R as in the conventional case is obtained in the region B. The area A is discontinuous with the area B and becomes a graph of the voltage drop amount Iph (x) × R having the same shape as that of the area B across the boundary portion (solid line graph in FIG. 4). .

  FIG. 5 is a graph showing the extinction characteristic of the conventional electroabsorption modulator when the value of the resistance R is constant in the section of x = 0 to x1. FIG. 6 is a graph showing the extinction characteristic of the electroabsorption modulator MD according to the present embodiment having a resistance value different from those of R1 and R2. 5 and 6, the vertical axis represents the logarithmic ratio (unit: decibel) of light intensity, and the horizontal axis represents the voltage V1 applied from the outside.

  In the case of FIG. 5 in which the value of the resistance R is constant in the section of x = 0 to x1, at the position of x = 0 where the value of the photocurrent Iph (x) is large, x = x1 where the photocurrent Iph (x) is small. The applied voltage VMQW to the light absorption layer is smaller than at the position. Since the light absorption phenomenon in the light absorption layer occurs with an increase in the applied voltage VMQW to the light absorption layer, the extinction characteristic with respect to the external application voltage V1 at x = 0 is more than the extinction characteristic with respect to the external application voltage V1 at x = x1. Is also shifted in the increasing direction of the externally applied voltage V1.

  When expressed as a logarithmic ratio of the light intensity as shown in FIG. 5, the extinction characteristic of the entire electroabsorption modulator is represented by the sum of the extinction characteristics in each region of x = 0 to x1. Therefore, the extinction characteristic of the whole electroabsorption modulator does not have steepness with respect to the externally applied voltage V1, as can be seen from FIG. As a result, the extinction ratio and transmission characteristics of the modulation waveform of the optical signal are greatly degraded.

  On the other hand, in the case of FIG. 6 in which the resistance values between the regions A and B are different from those of R1 and R2, the average extinction characteristic with respect to the externally applied voltage V1 in the region A and the average extinction property with respect to the externally applied voltage V1 in the region B. Is not much different. Therefore, the sum of the average extinction characteristics in each of the areas A and B, that is, the extinction characteristics of the entire electroabsorption modulator is more uniform as the extinction characteristics in the areas A and B are uniform as shown in FIG. It becomes steep with respect to the externally applied voltage V1.

  That is, as described above, in each of the first semiconductor layer region having the resistance R1 between the anode and the cathode and the second semiconductor layer region having the resistance R2 between the anode and the cathode, the photocurrent (Iph1) In the semiconductor layer region (first semiconductor layer region) whose strength is relatively larger than the strength of the photocurrent (Iph2) in the other semiconductor layer region (second semiconductor layer region), the resistance in the direction between the anode and the cathode The value of (R1) is relatively small, and the intensity of the photocurrent (Iph2) in each of the first and second semiconductor layer regions is the photocurrent (Iph1) in the other semiconductor layer region (first semiconductor region). In the semiconductor layer region (second semiconductor layer region) which is relatively small compared to the strength of, the resistance (R2) in the direction between the anode and the cathode is relatively large. Therefore, it is possible to make the voltage drop Iph (x) × R calculated by the product of the photocurrent Iph (x) and the resistance R uniformly close at each position in the traveling direction D1 of the incident light. The voltage VMQW applied to the absorption layer 104 can be made uniform in the light traveling direction D1. As a result, it is possible to obtain an electroabsorption modulator having improved extinction characteristics as an optical modulator and a semiconductor device in which the electroabsorption modulator is formed.

  Also, a plurality of semiconductor layer regions having different resistance values (a first semiconductor layer region having a resistance R1 and a second semiconductor layer region having a resistance R2) are arranged so as to be aligned in the traveling direction D1 of incident light. ing. Therefore, the voltage VMQW applied to the InGaAsP light absorption layer 104 can be made close to uniform in the light traveling direction D1 by appropriately arranging a plurality of semiconductor layers at each position in the traveling direction D1 of incident light.

  Further, the values of the resistances R1 and R2 in the direction between the anode and the cathode of the semiconductor layer are in a plurality of semiconductor layer regions (the first semiconductor layer region having the resistance R1 and the second semiconductor layer region having the resistance R2). It differs depending on the concentration of impurities contained. Therefore, the electroabsorption modulator according to this embodiment can be easily manufactured by appropriately controlling the impurity implantation amount.

  The vertical cross-sectional shapes of the first and second semiconductor layers with respect to the light traveling direction D1 are the same at each position in the traveling direction D1. Therefore, there is no difference in the physical shape of the semiconductor layer in the light traveling direction D1, and manufacturing is easy.

  Next, a method for manufacturing the semiconductor device of FIG. 1 will be described. First, as shown in FIG. 7, an n-type InP guide layer 101, an InGaAsP laser active layer 102, and a p-type InP guide layer 103 are formed on a semiconductor substrate 100 as an n-type InP substrate by a CVD (Chemical Vapor Deposition) method or the like. The layers are stacked in this order. Thereafter, as shown in FIG. 8, portions of the InGaAsP laser active layer 102 and the p-type InP guide layer 103 located in the formation region of the electroabsorption modulator MD are removed using a photolithography technique and an etching technique.

  Next, as shown in FIG. 9, the InGaAsP light absorption layer 104 and the p-type or i-type InP guide layer 105 are selectively formed only in the removed portion by using a photolithography technique and a CVD method. Thereafter, a portion of the p-type or i-type InP guide layer 105 located in the formation region of the p-type InP guide layer 110 is removed using a photolithography technique and an etching technique.

  Next, as shown in FIG. 10, the p-type InP guide layer 110 is formed in the removed portion of the p-type or i-type InP guide layer 105 by using a photolithography technique and a CVD method. Then, impurities are implanted into the p-type InP guide layer 110 by an ion implantation technique so that the resistance value of the p-type InP guide layer 110 is lower than the resistance value of the p-type or i-type InP guide layer 105. The impurity concentration of the p-type InP guide layer 110 is increased.

  When a so-called buried structure is employed, the n-type InP guide layer 101, the InGaAsP laser active layer 102, the p-type InP guide layer 103, the InGaAsP light absorption layer 104, the p-type InP guide layer 110, and the p-type or i-type In order to form a stacked structure of the type InP guide layer 105 in a ridge shape, a current blocking layer (not shown in the cross-sectional view of the present application, not shown) is embedded around the portion to become the ridge. Thereafter, as shown in FIG. 11, a p-type InP cladding layer 106 is formed by a CVD method or the like.

  In the case of adopting a so-called ridge waveguide structure, the p-type InP guide layer 110 does not need to be formed as described above because there is no need to embed a current blocking layer. In that case, the p-type InP cladding layer 106 is buried instead of the p-type InP guide layer 110 in FIG. 11, and the impurity concentration of the p-type InP cladding layer 106 is changed to the p-type or i-type InP guide layer 105. Larger than that. If the portion of the p-type InP guide layer 110 is sufficiently small, the surface of the p-type InP clad layer 106 has almost no unevenness.

  Next, a p-type InGaAs film 107 is formed on the surface of the p-type InP clad layer 106, and p-type InGaAs contact layers 107a and 107b are patterned using a photolithography technique and an etching technique (FIG. 12).

Then, a SiO ₂ insulating film is formed on the p-type InGaAs contact layers 107a and 107b by a CVD method or the like, and using a photolithography technique and an etching technique, as shown in FIG. 12, a laser LD and an electroabsorption modulator. The SiO ₂ insulating films 108a to 108c are left only at the periphery of the electrical isolation portion with the MD and only at the ends of the p-type InGaAs contact layers 107a and 107b.

  Thereafter, anodes 109a and 109b are formed on the p-type InGaAs contact layers 107a and 107b, respectively, as shown in FIG. Similarly, the cathode 117 is formed on the back surface of the semiconductor substrate 100.

  In this embodiment, the structure of the modulator having two regions having different resistance values is shown. However, the structure having three or more regions having different resistance values, or the resistance values are not discontinuous but continuous. It goes without saying that even a structure that changes to the above has the effect of the present invention. Even if the resistance value is not monotonically increased along the light traveling direction, the resistance value is small at a portion where the intensity of the incident light is substantially relatively large and large at a portion where the intensity of the incident light is relatively small. As long as the voltage VMQW applied to the modulator has a distribution of resistance values such that the voltage VMQW approaches more uniformly than a modulator having the same resistance value in the light traveling direction. Needless to say, the present invention has the effects of the present invention.

<Embodiment 2>
The present embodiment is a modification of the semiconductor device according to the first embodiment, and does not form the p-type InP guide layer 110 in the first embodiment, but as shown in FIG. An impurity such as Zn functioning as a p-type dopant is diffused in a part of the type InP guide layer 105 to form the low resistance region 111. Note that the structure above the p-type InP cladding layer 106 is formed after FIG. 14 in the same manner as in the first embodiment.

  Even in this case, the resistance value is small at a location where the photocurrent intensity is relatively large and large at a location where the photocurrent intensity is relatively small, and the first semiconductor layer region (low There is a resistance region 111, a portion straddling the cladding layer 106 and the contact layer 107b), and a second semiconductor layer region (a portion straddling the p-type or i-type InP guide layer 105, the cladding layer 106 and the contact layer 107b). Similar to the first embodiment, these semiconductor layer regions are arranged so as to be aligned in the traveling direction of incident light.

  In the present embodiment, since impurities such as Zn are diffused in the low resistance region 111, the impurity composition of the low resistance region 111 is different from the impurity composition of the p-type or i-type InP guide layer 105. ing. That is, it can be said that the composition of the contained impurities differs between the first and second semiconductor layer regions.

  As described above, in this embodiment, a difference is provided in the resistance values of the first and second semiconductor layer regions by making the compositions of the impurities contained in the first and second semiconductor layer regions different. ing. Therefore, the semiconductor device according to this embodiment can be easily manufactured by appropriately selecting the type of impurity.

<Embodiment 3>
This embodiment is also a modification of the semiconductor device according to the first embodiment. In FIG. 15, after forming the p-type InGaAs film 107 for the p-type InGaAs contact layers 107a and 107b in the first embodiment, FIG. As shown, a low resistance region 112 is formed by diffusing impurities such as Zn into a part of the p-type or i-type InP guide layer 105, the p-type InP clad layer 106 and the p-type InGaAs film 107. Is. From FIG. 15 onward, the structure above the p-type InGaAs film 107 is formed in the same manner as in the first embodiment.

  Even in this case, the resistance value is small at a location where the photocurrent intensity is relatively large and large at a location where the photocurrent intensity is relatively small, and the first semiconductor layer region (low There is a resistance region 112) and a second semiconductor layer region (a portion straddling the p-type or i-type InP guide layer 105, the clad layer 106, and the contact layer 107b), and these semiconductor layer regions are used to advance incident light. The point that they are arranged in the direction is the same as in the first embodiment.

  Also in this embodiment, since impurities such as Zn are diffused in the low resistance region 112, the impurity composition of the low resistance region 112 is p-type or i-type InP guide layer 105, p-type InP cladding layer. 106 and the impurity composition of the film 107 are different. That is, it can be said that the composition of the contained impurities differs between the first and second semiconductor layer regions.

  As described above, also in this embodiment, a difference is provided in the resistance values of the first and second semiconductor layer regions by making the compositions of the impurities contained in the first and second semiconductor layer regions different. ing. Therefore, the semiconductor device according to this embodiment can be easily manufactured by appropriately selecting the type of impurity.

<Embodiment 4>
The present embodiment is also a modification of the semiconductor device according to the first embodiment. Instead of forming the p-type InP guide layer 110 in the first embodiment, as shown in FIG. A high resistance region 113 is formed by diffusing or ion-implanting an impurity killer such as proton into a part of the type InP guide layer 105 on the laser beam emitting end side. In FIG. 16 and subsequent figures, the structure above the p-type InP cladding layer 106 is formed in the same manner as in the first embodiment.

  Even in this case, the resistance value is small at a location where the photocurrent intensity is relatively large and large at a location where the photocurrent intensity is relatively small, and the first semiconductor layer region (p Type or i-type InP guide layer 105, a portion straddling the cladding layer 106 and the contact layer 107b), and a second semiconductor layer region (a portion straddling the high resistance region 113, the cladding layer 106 and the contact layer 107b), Similar to the first embodiment, these semiconductor layer regions are arranged so as to be aligned in the traveling direction of incident light.

  In this embodiment, since an impurity killer such as proton is diffused in the high resistance region 113, the impurity composition of the high resistance region 113 is the impurity composition of the p-type or i-type InP guide layer 105. Is different. That is, it can be said that the composition of the contained impurities differs between the first and second semiconductor layer regions.

  As described above, also in this embodiment, a difference is provided in the resistance values of the first and second semiconductor layer regions by making the compositions of the impurities contained in the first and second semiconductor layer regions different. ing. Therefore, the semiconductor device according to this embodiment can be easily manufactured by appropriately selecting the type of impurity.

<Embodiment 5>
The present embodiment is also a modification of the semiconductor device according to the first embodiment. Instead of forming the p-type InP guide layer 110 in the first embodiment, as shown in FIG. A high-resistance region 114 is formed in a part of the surface of the type InP guide layer 105, which is implanted with low-concentration impurities or is composed of an undoped InP layer or the like. From FIG. 17 onward, the structure above the p-type InP cladding layer 106 is formed in the same manner as in the first embodiment.

  Even in this case, the resistance value is small at a location where the photocurrent intensity is relatively large and large at a location where the photocurrent intensity is relatively small, and the first semiconductor layer region (p And a second semiconductor layer region (p-type or i-type InP guide layer 105, high-resistance region 114, clad layer 106, and contact) The portion extending over the layer 107b is present, and the semiconductor layer regions are arranged so as to be aligned in the traveling direction of the incident light, as in the first embodiment.

  Further, in this embodiment, since the high resistance region 114 is added, it can be said that at least one of the concentration and the composition of the contained impurities is different between the first and second semiconductor layer regions.

  As described above, in this embodiment, the resistance of the first and second semiconductor layer regions is made different by changing at least one of the concentration and the composition of the impurities contained in the first and second semiconductor layer regions. There is a difference in value. Therefore, the semiconductor device according to this embodiment can be easily manufactured by appropriately controlling the impurity implantation amount or selecting the type of impurity.

<Embodiment 6>
This embodiment is also a modification of the semiconductor device according to the first embodiment, and not only the formation region of the p-type InP guide layer 110 in the first embodiment, but also a part of the InGaAsP light absorption layer 104 therebelow. Is removed once using a photolithography technique and an etching technique, and a new InGaAsP light absorption layer region 115 and a p-type InP guide layer 116 shown in FIG. 18 are formed in that portion. Then, at least one of the impurity concentration and the composition in the new InGaAsP light absorption layer 115 is set to be different from that of the InGaAsP light absorption layer 104. Further, at least one of the impurity concentration and the composition in the new p-type InP guide layer 116 is also set to be different from that of the p-type or i-type InP guide layer 105. From FIG. 18 onward, the structure above the p-type InP cladding layer 106 is formed in the same manner as in the first embodiment.

  Even in this case, the resistance value is small at a location where the photocurrent intensity is relatively large and large at a location where the photocurrent intensity is relatively small, and the first semiconductor layer region (p And a second semiconductor layer region (portion straddling the p-type or i-type InP guide layer 105, the clad layer 106, and the contact layer 107b). However, the semiconductor layer regions are arranged in the traveling direction of the incident light in the same manner as in the first embodiment.

  As described above, also in this embodiment, the resistance of the first and second semiconductor layer regions can be reduced by making the concentration and composition of the impurities contained in the first and second semiconductor layer regions different. There is a difference in value.

  In the present embodiment, also in the light absorption layer, the first light absorption layer region (InGaAsP light absorption layer 115) and the second light absorption layer having different resistance values in the direction between the anode 109b and the cathode 117. A region (InGaAsP light absorption layer 104) is included, and the first and second light absorption layer regions are arranged in the traveling direction of incident light.

  Therefore, by appropriately disposing the first and second light absorption layer regions at each position in the traveling direction of incident light, it is possible to make the voltage applied to the light absorption layer uniform in the light traveling direction. .

  Then, in the first and second semiconductor layer regions and the first and second light absorption layer regions, it is possible to easily perform the present process by appropriately performing at least one of selection of the impurity type and control of the impurity implantation amount. The semiconductor device according to the embodiment can be manufactured.

1 is a diagram illustrating a semiconductor device according to a first embodiment. It is a graph which shows the relationship between a photocurrent and the distance in an electroabsorption type modulator. It is a graph which shows the relationship between the voltage applied between an anode electrode and a cathode electrode, and the distance in an electroabsorption type modulator in the conventional electroabsorption type modulator. FIG. 4 is a diagram in which the conventional electroabsorption modulator in the graph of FIG. 3 is compared with the electroabsorption modulator of the first embodiment. It is a graph which shows the extinction characteristic of an electroabsorption type modulator in case the value of resistance is constant. It is a graph which shows the extinction characteristic of an electroabsorption type modulator in case the value of resistance differs. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a step of the method of manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a semiconductor device according to a second embodiment. FIG. FIG. 6 illustrates a semiconductor device according to a third embodiment. FIG. 6 illustrates a semiconductor device according to a fourth embodiment. FIG. 10 is a diagram illustrating a semiconductor device according to a fifth embodiment. FIG. 10 illustrates a semiconductor device according to a sixth embodiment.

Explanation of symbols

100 semiconductor substrate, 101 n-type InP guide layer, 102 InGaAsP laser active layer, 103, 110, 116 p-type InP guide layer, 104, 115 InGaAsP light absorption layer, 105 p-type or i-type InP guide layer, 106 p-type InP cladding layer, 107a, 107 b p-type InGaAs contact layer, 108 a to 108 c SiO ₂ insulating film, 109a, 109b anode, 111, 112 low-resistance region, 113 and 114 high resistance region, 117 a cathode.

Claims (6)

A semiconductor substrate;
A light absorption layer formed on a surface of the semiconductor substrate, which is capable of absorbing a part of incident light by applying a voltage and outputs the incident light in a predetermined direction;
A semiconductor layer formed on the surface of the light absorption layer;
An anode formed on a surface of the semiconductor layer;
A cathode formed on the back surface of the semiconductor substrate;
The semiconductor layer includes a plurality of semiconductor layer regions having different resistance values in the direction between the anode and the cathode,
In each of the plurality of semiconductor layer regions, a photocurrent based on the incident light is generated,
In each of the plurality of semiconductor layer regions, in the semiconductor layer region where the intensity of the photocurrent is relatively larger than the intensity of the photocurrent in the other semiconductor layer region, the resistance in the direction between the anode and the cathode The value is relatively small,
In each of the plurality of semiconductor layer regions, the resistance of the resistance in the direction between the anode and the cathode in the semiconductor layer region in which the intensity of the photocurrent is relatively smaller than the intensity of the photocurrent in the other semiconductor layer region. Electroabsorption modulator with a relatively large value. The electroabsorption modulator according to claim 1,
An electroabsorption modulator in which the plurality of semiconductor layer regions are arranged so as to be aligned in the traveling direction of the incident light. The electroabsorption modulator according to claim 1,
The light absorption layer includes a plurality of light absorption layer regions having different resistance values in the direction between the anode and the cathode,
An electro-absorption modulator in which the plurality of light absorption layer regions are arranged in the traveling direction of the incident light. The electroabsorption modulator according to claim 2 or claim 3, wherein
The resistance value in the direction between the anode and the cathode of the semiconductor layer or the resistance value in the direction between the anode and the cathode of the light absorption layer is determined by the plurality of semiconductor layer regions or the plurality of light absorption layers. Different electroabsorption modulators due to different concentrations and / or compositions of impurities contained in the regions. The electroabsorption modulator according to claim 1,
The shape of the vertical cross section of the semiconductor layer with respect to the traveling direction of the incident light is an electroabsorption modulator that is the same at each position in the traveling direction. The electroabsorption modulator according to any one of claims 1 to 5,
A semiconductor device comprising: a laser formed on the semiconductor substrate adjacent to the electroabsorption modulator.

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